Investigations this year will include studies of the response of cardiac contractile proteins to afterload and to compare the synthetic responses to those seen with the stress of preload. The contractile proteins studied will include myosin and its subunit light and heavy chains, actin, tropomyosin, troponin and its subunits. The trigger mechanism initiating protein synthesis alterations in stress will be examined with the studies of the cytoplasmic substance (s) required for nuclear polymerase II activity stimulation demonstrated with increases in hydrostatic pressure. In addition, nuclei will be isolated from separated myocytes so that connective tissue and endothelial nuclei will be eliminated from the study. The differences, if any, in the sequential changes following preloading the heart including nuclear polymerase activity, RNA synthesis, protein synthesis will be determine and compared to those already seen with afterloading.